1. Field of the Invention
The present invention relates to certain radioopaque hexoses visualizable by computerized axial tomography (CAT) scanning and, more particularly, to a method of metabolic mapping using the same.
2. Description of the Background
With an increased understanding of cerebral energetics, it has become clear that cerebral function and energy metabolism are linked. Thus, knowledge of the rate of energy consumption or utilization should provide a significant insight into cerebral function both at the level of the whole brain and of the individual structures therein.
The energy requirements of nervous tissue, in general, are high. In fact, nervous tissue has a rate of oxidative metabolism which is almost as great as tissues which participate in processes requiring inordinate amounts of energy, such as mechanical work, osmotic work or extensive biosynthesis. See Cerebral Energy Metabolism and Metabolic Encephalopathy, Edited by D. W. McCandless.
Although glucose is not the only source of cerebral energy, it is the major source. Investigations involving glucose transport across the bloodbrain barrier have suggested that a significant correlation, by region, exists between glucose influx and utilization. See McCandless, id. This seems to suggest that the glucose supply provided to individual cerebral structures is in accordance with their respective metabolic requirements.
A technique allowing the determination of the rate of flux of such nutrients into specific anatomical structures of the brain would be expected to provide a window to a most dynamic process. As applied to a human brain, such a technique would, in essence, provide a potential bridge across the heretofore unbridgeable conceptual gap between the brain as a physical object and mental consciousness. Up until the present, subtle changes in consciousness have been, necesarily, inferred circumstantially from the effects of drugs, for example, believed to act upon the brain. While some efforts have been made to establish correlations between brain function, structure and consciousness, the underlying linking principles remain unknown.
To be sure, some attempts have been made to metabolically map the mammalian central nervous system. However, the principal means utilized has been positron emission tomography (PET). Typically, this technique entails the following procedure.
First, a sugar derivative of glucose which has been labelled with a positron emitter and is in addition incapable of fueling the Embden-Meyerhof pathway, is obtained for use as a tracer material. The glucose derivative is injected into the body to be metabolically mapped. Since glucose is the basic fuel for energy of metabolism, and is absorbed by cells in proportion to metabolic activity, the result of injecting the glucose derivative into the body is that the glucose derivative accumulates in areas of high metabolic activity, for example, local areas within the brain. These areas of high metabolic activity, which then contain the labelled derivative, may be visualized by the use of positron emission tomography.
However, PET suffers from a number of serious disadvantages which, to cite a few, are:
(1) the positron emitter, having a short half life, must be produced by bombardment with a cyclotron; PA0 (2) the emitter (usually F.sup.18) must be attached to the glucose derivative chemically; PA0 (3) since the emitter has a short half life, the cyclotron production and chemical coupling, and subsequent injection into the patient, must be performed rapidly, and this is very difficult since it requires the coordination of several specialists, and the cyclotron must be on-site with the patient and the PET instrument; and PA0 (4) there are less than 100 such PET scanners in the world, and therefore the technique is limited to a very few geographical locations.
Hence, a need continues to exist for a method for metabolic mapping of the mammalian central nervous system, which suffers from none of the disadvantages attendant to PET scanning, and which, moreover, provides a safe means for accomplishing the same.